In recent years, a hydraulic equipment including a plurality of swash plate type piston pumps has been put to practical use. As a regulator for changing the capacity of each swash plate type piston pump included in the hydraulic equipment, an electrical regulator and a hydraulic regulator are used.
FIG. 5 is a hydraulic circuit diagram showing a hydraulic circuit of a pump equipment 2 including electrical regulators 1 of a first prior art. The pump equipment 2 includes a pump apparatus 4 having two swash plate type piston pumps 3, and two electrical regulators 1. The pump apparatus 4 is a tandem pump in which two variable displacement type swash plate type piston pumps 3 are disposed in parallel with each other in an axial direction. Each swash plate type piston pump 3 is a variable displacement type piston pump capable of changing a capacity thereof in accordance with an inclination angle of a swash plate 5. The electrical regulator 1 is a regulator which is disposed for each swash plate type piston pump 3 and changes the capacity of the swash plate type piston pump 3 in accordance with an electrical signal input thereto.
For each swash plate type piston pump 3, a servo mechanism 6 is disposed to change the capacity of the swash plate type piston pump 3. Each servo mechanism 6 includes a servo piston 7. The servo mechanism 6 activates the servo piston 7 in accordance with the pressure of a mechanism driving oil supplied to the servo mechanism 6 to incline the swash plate 5 and to thereby change the inclination angle of the swash plate 5. Thus, the servo mechanism 6 changes the capacity of the swash plate type piston pump 3.
The electrical regulator 1 basically includes a servo switching valve 8, an electrical control type pilot piston 9 and a solenoid valve 10. The servo switching valve 8 includes a spool 11 and a sleeve 12. The electrical regulator 1 is configured to be able to receive pilot oil for activating the electrical control type pilot piston 9. The electrical control type pilot piston 9 is disposed to be able to receive the pressure of the pilot oil. The electrical control type pilot piston 9 displaces the spool in accordance with the pressure of the pilot oil to change a supply status of the mechanism driving oil supplied to the servo mechanism 6, thus changing the capacity of the swash plate type piston pump 3. The sleeve 12 is coupled to the servo piston 6 via a connecting rod 13 and controls the supply status of the mechanism driving oil based on the inclination angle of the swash plate 5, thus changing the capacity of the swash plate type piston pump 3. The solenoid valve 10 is configured to be able to change a connection status of an output port 14 thereof and a connection status of an input port 15 thereof in accordance with an electrical signal input thereto. The solenoid valve 10 changes the supply status of the pilot oil, having been supplied to the input port 15, with respect to the electrical control type pilot piston 9. A pipe for directing the pilot oil from a hydraulic supply source to the input port 15 of the solenoid valve 10 is formed for each electrical regulator 1 (see Patent Document 1 for example).
A hydraulic equipment of a second prior art includes a pump apparatus having two swash plate type piston pumps, and two hydraulic regulators. As with the first prior art, the pump apparatus is a tandem pump in which two swash plate type piston pumps are disposed in parallel with each other in an axial direction. For each swash plate type piston pump, a servo mechanism is disposed. The hydraulic regulator is a regulator which is disposed for each swash plate type piston pump and changes the capacity of the swash plate type piston pump in accordance with a hydraulic signal input to the hydraulic regulator, that is, the pressure of the pilot oil supplied to the hydraulic regulator. As with the electrical regulator, the hydraulic regulator basically includes a servo switching valve, and further includes a hydraulic control type pilot piston and a power control piston.
The hydraulic regulator is configured to be able to receive the pilot oil for activating the hydraulic control type pilot piston. The hydraulic control type pilot piston displaces the spool in accordance with the pressure of the pilot oil supplied to the hydraulic regulator and changes the supply status of the mechanism driving oil supplied to the servo mechanism. The power control piston is disposed to be able to receive the pressure of the hydraulic oil discharged from the swash plate type piston pump. The power control piston displaces the spool in accordance with the pressure of the hydraulic oil discharged from the swash plate type piston pump to change the capacity of each of two swash plate type piston pumps. Further, the power control piston is disposed to be able to receive the pressure of power control piston driving oil supplied thereto. The power control piston can displace the spool in accordance with the pressure of the power control piston driving oil to change the capacity of the swash plate type piston pump, thus changing a maximum power of the hydraulic oil discharged. Formed in the pump apparatus of the pump equipment is an inter-pump passage for directing the power control piston driving oil from the power control piston of one of the hydraulic regulators to the power control piston of another hydraulic regulator. With this, the pump equipment can supply the power control piston driving oil from one hydraulic supply source to respective power control pistons.                Patent Document 1: Japanese Patent Publication No. 3080597 (page 6, FIG. 16)        